MIT Technology Review: Wireless Power for Minuscule Medical Implants

InsightaaS: One of the key challenges associated with the 'Internet of Things' is power - how much electricity will be needed to power billions of new devices, and how will we distribute that electricity to devices that are located in hard-to-reach areas, ranging from sensors beneath the sea to implants within our bodies?

In July, InsightaaS featured an MIT Technology Review article looking at the power demands associated with IoT. Today, we return to MIT Technology Review for the other part of the story: possible means of powering implanted devices. The article notes that there are many potential uses for these gadgets ("regulate insulin levels, control appetite, lower blood sugar, or treat brain injuries"), but that batteries are too bulky to implant alongside this array of electronics, and that current wireless methods of distributing power to devices placed just under the skin "won’t work with devices buried deep in the body."

The post then highlights research from a team at Stanford, which is working on a "midfield wireless powering" approach that gets around the near-field constraint in which power "decays exponentially with distance" from an external source. The new method is far from efficient - in a test with pacemakers in rabbits, the Stanford team, led by electrical engineer Ada Poon, achieved "0.1 percent efficiency–meaning that nearly all the energy sent from the conductive material to the pacemaker was wasted." However, the energy thatwas successfully transmitted is sufficient to run a low-power medical device, and "met safety regulations limiting the amount of radiation delivered to a given amount of tissue in humans" - an extremely important issue when we look forward to an IoT future in which devices are all around (and within) us!

Medical implants like pacemakers, deep brain stimulators, and cochlear implants could someday be joined by still more bioelectronic gadgets–devices that regulate insulin levels, control appetite, lower blood sugar, or treat brain injuries (see "Nerve-Stimulating Implant Could Lower Blood Pressure").

But before we’re all riddled with electronics, researchers have to figure out how to power it all. Pacemaker batteries are too clunky for tiny devices saddled up to nerves, and existing wireless methods, such as those used for cochlear implants, won’t work with devices buried deep in the body.

That’s where electrical engineer Ada Poon and her team at Stanford University say they might be able to help. The group has developed a new method of sending magnetic fields well below skin level to power devices that would otherwise need batteries.

Wireless systems like the one used in cochlear implants sit permanently on the skin and derive power from electromagnetic induction, in which a current running through a coil of wire generates a magnetic field that then induces a current in a nearby device. The problem is that a field generated this way decays exponentially with distance from the generating coil, so it only works with devices close to the skin’s surface...

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